Chapter 3: Amount of substance (3.1-3.4)

Question 1

Water of crystallisation

Answer 1

water molecules that form an essential part of the crystalline structure of a compound.

Question 2

Moles =

Answer 2

mass / Mr

Question 3

How do you work out the water of crystallisation?

Answer 3

1) Calculate the amount, in mol, of the anhydrous salt formed
2) Calculate the mass and amount , in mol, of water
3) Divide by the smallest number of moles: simplest whole number ratio
4) Write down the value of X and write in the formula of the salt

Question 4

Avogadros constant

Answer 4

6.02x10^23

Question 5

Anhydrous

Answer 5

a substance containing no water molecules

Question 5

Hydrated

Answer 5

Crystalline and containing water molecules

Question 6

Why may the mass of anhydrous salt not be what you expected after heating?

Answer 6

1) Some of the water may not have been removed

2) Heating could have caused the salt to decompose

Question 7

Ideal gas equation

Answer 7

pV = nRT
p = pressure in Pa
V = volume in M[3]
n = number of moles
R = the gas constant 8.31Jk[-1]mol[-1]
T = temperature in K

Question 8

Likely conversions to be made when using ideal gas equation

Answer 8

Cm3 -> m3 = 10^-6
Dm3 -> m3 = 10^-3
°C -> K = +273
kPa -> Pa = 10^-3

Question 9

Why are reactions with high atom economies good?

Answer 9

1) Produce a large proportion of desired products and few unwanted waste products
2) Important for sustainability as they make the best use out of natural resources

Question 10

Atom economy equation

Answer 10

atom economy (%) = (sum of molar masses in desired product / molar masses of all products) X 100

Question 11

% yield equation

Answer 11

(useful output/total input) X 100

Question 12

Gas calculations at RTP

Answer 12

volume (dm[-3]) = moles (n) X 24

Question 13

Working out Mr from density

Answer 13

Mr = density x 24000